#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>

#define DELIM " \t"
#define LINE_SIZE 1024
#define ARGC_SIZE 32
#define EXIT_CODE 44

int lastcode = 0;
int quit = 0;
extern char **environ;
char commandline[LINE_SIZE];
char *argv[ARGC_SIZE];
char pwd[LINE_SIZE];

char myenv[LINE_SIZE];


const char* getusername()
{
  return getenv("USER");
}

const char* gethostname()
{
  return getenv("HOSTNAME");
}

void getpwd()
{
  getcwd(pwd,sizeof(pwd));
}

 

void interact(char* cline,int size)
{
  getpwd();
  printf("[MTSHELL:%s@%s %s] #",getusername(),gethostname(),pwd);
  char* s=fgets(cline,size,stdin);
  assert(s);
  (void)s;
  cline[strlen(cline)-1]='\0';
}

int splitstring(char cline[],char *_argv[])
{
  int i=0;
  argv[i++]=strtok(cline,DELIM);
  while(_argv[i++]=strtok(NULL,DELIM));
  return i-1;
}

void normalexcute(char* _argv[])
{
  pid_t id=fork();
  if(id<0)
  {
    perror("fork");
    return;
  }
  else if(id==0)
  {
    execvp(_argv[0],_argv);
    exit(EXIT_CODE);
  }
  else 
  {
    int status=0;
    pid_t rid=waitpid(id,&status,0);
    if(rid==id)
    {
      lastcode=WEXITSTATUS(status);
    }
  }
}

int buildcommand(char* _argv[],int _argc)
{
  //特判
  if(_argc==2&&strcmp(_argv[0],"cd")==0)
  {
    chdir(argv[1]);
    getpwd();
    sprintf(getenv("PWD"),"%s",pwd);
    return 1;
  }
  else if(_argc==2&&strcmp(_argv[0],"export")==0)
  {
    strcpy(myenv,_argv[1]);
    putenv(myenv);
    return 1;
  }
  else if(_argc==2&&strcmp(_argv[0],"echo")==0)
  {
    if(strcmp(_argv[1],"$?")==0)
    {
      printf("%d\n",lastcode);
      lastcode=0;
    }
    else if(*_argv[1]=='$')
    {
      char* val=getenv(_argv[1]+1);
      if(val)
      {
        printf("%s\n",val);
      }
    }
    else 
    {
      printf("%s\n",_argv[1]);
    }
    return 1;
  }
  if(strcmp(_argv[0], "ls") == 0)
  {
    _argv[_argc++] = "--color";
    _argv[_argc] = NULL;
  }
  return 0;
}

int main()
{
  while(1){
  //用户交互
  interact(commandline,sizeof(commandline));

  //分割子串，解析命令行
  int argc=splitstring(commandline,argv);
  if(argc==0) continue;
  
  //判断指令
  int n=buildcommand(argv,argc);

  if(!n)
  {
    normalexcute(argv);
  }
  }
  return 0;
}
